Beyond Tier 4 Engines

For almost two decades, you’ve heard the EPA talk about tiers and emission regulations for high-horsepower, off-highway diesel engines. You’ve adjusted as engine technology changed and widened your vocabulary with phrases like selective catalytic reduction and exhaust gas recirculation.

In 2014, Tier 4 Final came into effect for engines from 174 hp. to 750 hp., and next year it will extend below and above these outputs. This is the last scheduled emission regulation, which begs the question: Will Tier 4 Final be the last emission regulation? And what can you expect next in engine technology?Tier 5 on the horizonAt this point, the EPA hasn’t issued anything saying there will be a Tier 5. But most industry experts believe there will be.

“Tier 5 is on the horizon,” says David Kohuth, product training specialist at New Holland. “I believe there will be a Tier 5,” confirms Antti Marttinen, manager of product management – global engine installations at AGCO. Cummins global off-highway communications director Kevan Browne agrees. “We are making plans now for a Tier 5, even though one doesn’t exist,” he says. “We are doing this on the basis that the European Union (EU) has proposed a Stage V. The proposal has gone to a high level, and we are almost 100% sure it will be introduced.”

Through Tier 4 Final and Stage IV, the EPA and the EU have aligned emissions regulations for high-horsepower diesel engines. “As Europe and North America are trying to synchronize as much as they can, we look at what we have compared to the EU and what they are doing at the moment,” explains Marttinen.

If you’ve kept up with your Tiers, you know Tier 4 and Tier 4 Final have reduced particulate matter (PM) and nitrogen oxide (NOx) emissions to near-zero levels. The proposed EU regulation will tighten NOx emissions to standards similar to the EPA and further reduce the particulate number by targeting the number of particulates, not just the mass or size.

“In addition to telling you the mass of particles you can emit, the EU is looking to establish a standard that says you can’t emit more than a certain volume of particles during a certain period of time,” explains Allen Schaeffer, executive director of the Diesel Technology Forum. The Diesel Technology Forum is a nonprofit educational organization that represents diesel engine and equipment manufacturers.

You’ll be relieved to hear that the solution for the further reduction is a known technology: a diesel particulate filter (DPF). At this point, only some Tier 4 Final engines use DPFs. “What Stage V will be is a DPF-enforcing regulation,” says Browne. “There is no other way.

“This regulation is about to be introduced for the European on-highway vehicles,” he adds. “All of the truck and bus engines will have to use a DPF.”

Diverging pathsThe big question is whether or not the U.S. will join Europe on its particulate mission, or if the EPA will decide to tackle greenhouse gas emissions as it has already done for on-highway trucks. The EPA aims to reduce greenhouse gases by increasing fuel efficiency, which reduces carbon dioxide (CO2) emissions.